852 CHATTAWAY : THE QUANTITATIVE CONVERSION OF

LXX1X.-The Quantitative Conuemion of Ayomatic Hydraxines into Diazoizium Salts.

By FREDERICK DANIEL CBATTAWAY.

THE primary aromatic hydrazines, which are so readily obtained from diazonium salts by reduction, might be expected t o be reconverted into the latter with similar ease by oxidation. This reconversion, however, has proved to be a matter of great difficulty, For it to take place, two hydrogen atoms of the *NH*NH, group must be replaced by hydroxyl groups, and, as the author has recently shown (Trans., 1907, 91, 1323 ; 1908, 93, 270), when one such group has been introduced the typical diazo-decomposition :

R*N*H I C N H + I + I l l + I R - ~ O H H N O*H

occurs so readily tha t even i n presence of acids comparatively in- significant amounts of diazonium salts are formed, whilst in presence of alkalis they are not produced at all.

Emil Fischer (Annalen, 1877, 190, 97) first showed that the reaction was posfiible, and recognised the presence of a diazonium salt among the products of the oxidation of phenylhydrazine sulphate by yellow mercuric oxide. The amount which can be thus formed is, however, very small, and, although Altschul (J. pr. Chena., 1896, [ii], 54, 496) found tha t a much larger yield could be obtained by employing nitrous acid as the oxidising agent, no really satisfactory method of effecting the reconversion has yet been described.

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AROMATlC HYDRAZINES INTO DIAZONIUM SALTS. 853

The author finds that all primary aromatic hydrazines can be quantitatively converted into the corresponding diazonium salts either by chlorine or by bromine."

If either halogen is allowed to act at a low temperature on the hydrazine dissolved in alcohol, the diazonium salt separates out in a pure state.

Unless, however, the solid salt is required, the operation can be more easily carried out by dissolving the hydrazine in glacial acetic acid, cooling the solution to about - 15O by addition of crushed ice, and either passing in a rapid stream of chlorine or adding the calculated quantity of bromine dissolved in acetic acid and similarly cooled by ice.

The formation of the solid diazonium salt is without doubt due to n substitution by halogen of two atoms of hydrogen in the *NH*NH, group, followed by the elimination of halogen acid, thus :

As in other cases where hydrogen attached to nitrogen is replaced by halogen, an additive product is probably first formed, in this instance by the addition of four halogen atoms, each nitrogen atom thus becoming quinquevalent. The successive elimination of three molecules of halogen acid then gives rise to the diazonium salt.

It seems probable that the removal of the last molecule of halogen acid, which is necessary for formation of the solid diazonium compounds, only takes place when the latter assume the solid state, and tha t when these compounds exist in solution or undergo any of the reactions which are characteristic of them they actually have the structure :

R*N*C1 R*N-CI R*N*Br R*N*Br or an d or

H*N*Cl H*#*Cl H*h*Br H. fi . Br * The relationship of the diazonium salts to the hydrazines and all

their reactions can be better explained on this hypothesis than on any other.

Action of Chlorine on Phenylhydraxine.

When chlorine is passed rapidly into a solution of phenylhydrazine kept a t a low temperature, action at once takes place; hydrogen is replaced by chlorine and hydrogen chloride is produced, but no nitrogen

* A large number of totally different products can be obtained from primary aromatic hydrazines by the aztion on them of the 'halogens according to the con- ditions under which the action takes place. A full treatment of the subject is reserved for a later communication ; in this paper, the production of diazoniiini salts is alone dealt with.

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854 CHAT TAWAY: THE QUANTITATIVE CONVERSION OF

is evolved, nor does any substitution in the ring take place, benzene- diazonium chloride and hydrogen chloride being the sole products.

If solid benzenediazonium chloride is to be prepared, it is best to operate in alcoholic solution, cooling with solid carbon dioxide, but if the salt is not required in the solid form the action can be much more easily carried out in acetic acid solution.

To prepare the solid diazonium salt, 5 grams of phenylhydrazine, freshly distilled and twice recrystallised, were dissolved in 100 C.C. of absolute alcohol, and cooled strongly by the addition of solid carbon dioxide, so much of the latter being added that a pasty mass was obtained. Through this a rapid stream of dry chlorine was passed until the whole was saturated, the semi-liquid mass being thoroughly stirred during the passage of the gas by the delivery tube. The liquid became pale yellow, and benzenediazonium chloride separated as a white solid. One hundred C.C. of dry ether, also strongly cooled and containing suspended solid carbon dioxide, were added, and a rapid current of dry air was aspirated through the mixture until the excess of chlorine and the solid carbon dioxide had been removed and the temperature of the liquid had risen to about - ZOO. The solid benzenediazonium chloride was then filtered off and well washed with dry ether.

The purity of the substance was established by a chlorine estimation, and also by converting it into benzeneazo-@-naphthol by coupling it with @-naphthol. The benzeneazo-F-naphthol thus obtained crystal- lised from alcohol in brilliant scarlet needles melting a t 135O, and was identical with a specimen prepared from benzenediazonium chloride prepared by diazotising aniline.

To prepare an acetic acid solution of the diazonium salt, 2.16 grams of phenylhydrazine, purified as before, were dissolved in 80 C.C. of glacial acetic acid and 40 grams of crushed ice added. A rapid stream of chlorine was passed through the liquid, stirring as before, until it was saturated and the gas escaped freely. No nitrogen was evolved, the action taking place quietly and quantitatively. The liquid a t first assumed a slightly red tint, which, however, disappeared as the passage of the chlorine was continued, a pale yellow liquid being finally obtained. To remove the excess of chlorine, more crushed ice was added, and air was drawn through the liquid until the odour of chlorine could not be detected. The benzenediazonium chloride produced was then estimated by conversion into benzeneazo-@-naphthol,* a quantita- tive yield of which, in a perfectly pure state, can be obtained in a carefully conducted experiment.

It is thus seen that no substitution in the benzene nuclew occurs

* A number of experiments made with weighed quantities of pure diazonium compounds showed that accurate results could be obtained by filtering off the azo- compound in a Gooch crucible and drying at 110".

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AROMATIC HYDRAZINES INTO DIAZONlUM SALTS. 855

under the conditions named, thesole product of the action of chlorine on phenylhydrazine being benzenediazonium chloride, which is produced in theoretical amount.

Action of Bromine on Phenylhydraxine. The action of bromine on phenylhydrazine is exactly similar to that

of chlorine, benzenediazonium bromide and hydrogen bromide alone being produced. Since the amount of bromine required can be accurately weighed, the operations are more easily carried out.

4.32 Grams of pure phenylhydrazine were dissolved in 50 C.C. of absolute alcohol and cooled by solid carbon dioxide, the latter being added in excess so as to form a semi-solid mass ; 12.8 grams of bromine were next mixed with 50 C.C. of absolute alcohol, similarly cooled and containing an excess of suspended solid carbon dioxide. The liquid containing the bromine was then quickly added to that containing the phenylhydrazine, and the two thoroughly stirred together. The mixture became pale yellow, and solid benzenediazonium bromide separated; 100 C.C. of dry ether were next added, and a current of air aspirated through the mixture, this being continued until the solid carbon dioxide had disappeared and the temperature had risen to about - 20". The benzenediazonium bromide was then filtered off and washed with dry ether. It was obtained as a white, crystalline powder, which in bulk was seen to have a faint jellow tint. On adding ether gradually to a solution of the salt in cold alcohol, i t separated in small, six-sided plates of a very faint yellow colour. Its purity was ascertained by a bromine estimation and by converting it as before in to benze neazo-P- n apht hol.

Unless the solid salt is required, it is, however, much simpler to work in glacial acetic acid solution, cooling by crushed ice. Phenyl- hydrazine can be so easily and rapidly converted into diazonium bromide in this way that the operation is excellently adapted for a lecture experiment.

The following is a convenient procedure : 2.16 grams of pure phenyl- hydrazine are dissolved in 40 C.C. of acetic acid, and 20 grams of crushed ice added; 6.4 grams of bromine are dissolved in 40 C.C.

of acetic acid and 20 grams of crushed ice added. The temperature of each liquid having fallen to about - 15", the two are rapidly mixed, the bromine solution being poured into the hydrazine solution, the latter being rapidly stirred ; some heat is developed, bnt the tempera- ture of the whole should not rise above - lo", as the ice still remains in excess if the operations are carried out quickly. A little benzene- diazonium perbromide is formed locally where the bromine is in excess, but this at once disappears on stirring, and a clear, pale yellow liquid is obtained, 110 nitrogen being evolved.

VOL. XCIII. 3 L

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856 CHATTAWAY: THE QUANTITATIVE CONVERSION OF

The clear liquid is next poured over a considerable excess of crushed ice, and made slightly alkaline by the cautious addition of a cold concentrated solution of potassium hydroxide. On adding /3-naphthol dissolved in dilute aqueous potassium hydroxide, benzeneazo-@naphthol is thrown down as a brilliant red precipitate. The yield in a carefully conducted experiment is theoretical. I n two test experiments, using the above quantity of phenylhydrazine, 4 9 and 6 grams of benzene- azo-P-naphthol were obtained, the amount which theoretically should be produced being 4.96 grams,

All primary aromatic hydrazines which have been studied are acted on by chlorine and bromine in a precisely similar manner, and the action appears to be a general one.

It may, however, again be noted that; the halogens can produce from the hydrazines a great variety of substances, as the hydrogen attached to the nitrogen is substituted atom by atom, and the nitrogen halogen derivatives formed can break down or transform in many different ways, depending on the conditions, As an illustration OF this, reference may be made to the observation of Michaelis (Be?'., 1893, 26, 2190), confirmed by Vaubel (J. pr. Chem., 1894, [ii], 49, 640; 1897, [ii], 55, 220), that, when phenylhydrazine or its acetyl derivative is brominated, in addition to a bromo-substituted hydrazine, a bromo-substituted diazonium salt is produced. Following up a statement made by Emil Fischer (Annalen, 1893, 272 ,214) that acetylphenylhydrazine can be directly brominated if dissolved in concentrated hydrochloric acid, Michaelis, by the direct action of bromine at the ordinary temperature on phenylhydrazine and acetylphenylhydrazine, prepared p-bromophenylhydrazine and 2 : 4-di- bromophenylhydrazine, and noted that, in addition, p-bromo- and 2 : 4-dibromo-benzenediazonium chloride were respectively produced,

The formation of these compounds is due to the substitution of hydrogen in the imino-group of the hydrazine by bromine, the action of the halogen on the amino-group being hindered, or rendered much less rapid, by the presence of the concentrated hydrochloric acid, this by combining with the group preventing the addition of halogen which must precede substitution, The nitrogen-bromide thus formed undergoes under the influence of the halogen acid the transformation characteristic of phenyl acyl nitrogen bromides, the halogen entering the ring in the para- and ortho-positions and forming the substituted hydrazine, for example :

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AROMATlC HYDRAZINES INTO DIXZONIUM SALTS. 857

HCl,NH,*N Br /\

HCI, N H,= NH /\

i i -+ I ) + - \/ \/

Br

HC 1, N H,*NBr HC1,NH;KH 7\ I -+

'.\/ Br

at each stage of this transformation a certain amount of the sub- stituted hydrazine is acted on in the manner described in this paper and converted into the correspondirtg diazonium salt.

Action of Cldorine and Bromine on 0- and p-Tolglhydrazine, p-Bromo- phe jtylh y druxine, p- Nitrophen ylhydrasine, I'lmzg Zliydruzine-p- 8u Zphoizic Acid, und P- N u ~ l ~ t l ~ y l h y d r ~ a i n e .

The action of chlorine and of bromine on these hydrazines has been investigated in a similar manner, and with similar results to those previously described. I n every case, the action oE the halogen at a low temperature converts the hydrazine into the corresponding diazonium salt .

The conversion in each of these cases is most conveniently effected by bromine carrying out the reaction in acetic acid, the amount of acid used and the details of procedure being suitably modified. I n no case, if the temperature is kept low, is halogen substituted in the aromatic residue, this only occurring in presence of mineral acids when the temperature is such as to allow transformation of the mono-halogen imino-substitution product to take place.

I n order to obtain a quantitative yield of diazonium salt in any of these reactions, it is necessary to work very carefully and to use accurately weighed amounts of pure bromine and recently purified hydkazine. All primary aromatic hy drazines are so readily oxidised by the oxygen of the air (Chattaway, Trans., 1907, 91, 1323) that unless purified by distillation under diminished pressure, or recryatal- lised not long before use, they are certain to contain brown-coloured oxidation products. Such slightly impure hydrazines do not give a perfectly clear solution of the diazonium compound, and small quanti- ties of brown solid, or eveu tarry matters, are thrown out on neutrali- sation. These, however, can be filtered off from the aqueous solution of the diazonium salt, the yield of the latter being slightly reduced. Working with ordinary care, however, it is easy to obtain a yield of 90-95 per cent. of the theoretical.

3 L 2

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858 CONVERSION OF HYDRAZINES INTO DIAZONIUM SALTS.

The author is indebted to the Government Grant Committee of the Royal Society for a grant, which has partly covered the cost of this investigation, and t o Dr. H. B. Baker for allowing him to use the Christ Church laboratory,

CHRIST CHURCH, OXFORD.

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